Creatures

Giant Killer - Really good at dealing with large threats, and a decent early blocker.  He can also shut down the opponents largest creature threat if he can stick around late game.

Seasoned Hallowblade - While I don't necessarily like tossing cards to his ability, if he resolves against certain lists he can really cause some issues since 3 power threatens relatively well and can set up stalled board states since they can't kill him as easily as the 1 toughness would make it appear.

Lavabrink Venturer - Really good against mono red by dodging a lot of their removal and can act as a doorstop against some really big threats on the board even late game.  Don't sleep on him.

Baneslayer Angel - Man, this card is just a really strong top end creature to beat your opponent to death with.  First strike is extremely viable, and the lifelink (while not super important with Nine Lives) is a very nice bonus.

Archon of Sun's Grace - Extremely powerful with the number of enchantments being run in this list.  Extra value off of removal spells is extremely welcome in control and Archon WILL flood the board super quickly if unchecked.  A really strong secondary win-won.

Yorion, Sky Nomad - Here for the 80 card deck, Yorion really helps with bounces on a few key targets.  While we don't run Charming Prince for shenanigans, bouncing our removal and targeting bigger threats, or bouncing an ECD to get an additional trigger out of it is amazing value.  Archon also really appreciates the extra triggers for Constellation.

Enchantments

Pacifism - Excellent early removal that can also cause headaches late game (a lot of the cards in this list can function regardless of board or game state).

Banishing Light - In the same boat as Pacifism, but hitting any permanent is a really nice bonus to it.  If they drop an Ugin before you Nine Lives yourself, please erase him from the board.

Runed Halo - Usually a sideboard card, this can actually swing games early or late (running theme here) by once more invalidating a big threat your opponent has on the board.

The Birth of Meletis - A good way to protect your early board state, hit your land drops and sustain.  A really nice addition to the early game.  This is one of the few cards it sucks to top deck if the game stalls out.

Elspeth Conquers Death - Excellent removal with some very high value cards that you can pull out of your graveyard.  Also works pretty well with Hallowblade since tossing a Baneslayer to keep him alive isn't the end of the world.

Nine Lives - The card that made me theory craft for mono white.  Running a full set of these is just plain rude against aggro, since by the time they manage to put 8 counters on one, you drop another and reset the clock.  This runs into problems against any sort of enchantment removal that avoids hexproof though, and will cost you games if you misplay it.  You've been warned.

Sorcery

Shatter the Sky - Good old non-situational removal.  Wipe away their scary board states and start from scratch.  Hallowblade can dodge this too with his ability.

Idyllic Tutor - A great tutor for this list since it runs 21 enchantments.  A really strong QoL upgrade that didn't fit in the 60 card list.

Artifact

Sorcerous Spyglass - One of the hard counters to this list is, unsurprisingly, Ugin, the Spirit Dragon.  This is our only surefire way of dealing with him since we don't have instant speed removal.  Wait for the Fae of Wishes to pull him out of the deck, or hedge your bets and play it early. 

Planeswalker

Elspeth, Sun's Nemesis - Running a single copy of Ellie to make use of her recursion and ability to flood the board or make your Baneslayer's bigger for the turn.  She also draws a good amount of hate, so an earlier drop to take some heat off isn't a terrible play either.

Mana Base

Running 35 lands here since the deck tops out at 5 CMC.  Triomes for the cycle and Temples for the scry.

This is essentially a sidegrade to my 60 card monowhite control list.  It has more options and a better quality of life with certain cards, but it's not nearly as consistent thanks to the Yorion clause.  Higher ceiling, lower floor.  Let me know what you think!

Edit:  Cut the singleton Elspeth and went to a full set of Shatter the Sky.  It helps us hit the needed boardwipe on turn 4 against aggro decks and feels a bit more impactful than Elspeth does when she comes down.